Production of sodium cyanate



Patented July 16, 1940 zgca on ,UNITED STATES OFFICE PRODUCTION OF:SODIUM OYANATE" Hermann Theodor Josef Kfinig, Dordrecht, Netherlands,assignor to -v Stikstofbindings igggztrie-Nedrland N. V.,' Dordrccht,Nether N Drawing. Application'oJuly ll, 1938; Serial No. 218,638. In theNetherlands July 1937 4 Claims. (01. 3-1-1 55 This invention relates tothe productionof If for instance a mixture of stoichiometric productscontaining sodium cyanate. proportions of sodium cyanate, and calcium Ithas been found that if a mixture of stoioxide is heated one hour to 600C. in a nitrogen chiometric proportions of alkaline earthcyanatmosphere, the reaction results in the formaamides and anhydroushigh percentage sodium tion of a product containing about 30% CaNCN, 5

5 sulfide is heated to elevated temperatures, 50- wherein about 76% ofthe cyanate-nitrogen indium cyanate and alkaline earth sulfides aretroduced is present as. cyanamide nitrogen; 3% formed, if the mixture iscaused to react in the a are converted into NaCN presence of carbondioxide. It is of no, avail whether in this reaction are When using amixture of calcium cyanamide formed sodiumhor calciumcyanamide, or'amix- 10 and anhydrous sodium sulfide the course of the ture of thesecompounds, according to the equareaetions, for instance at a temperatureof 500 tions;

0., may be expresseduoy the following equations. (wCaO+ZNaCNONaZNCN+CaCOS (a) CaNCNJrNa2S=Na2NCN+CaS (1c)CaO+2NaCNO=CaNCN+Na2CO3 (c) CaNCN+NaZS+COZ=2NaCNO+Cas This does nothowever influence the fact that the greater part of the'nitrogenintroduced as Instead ofrsodw-m slfufide addltmn to sodium i cyanate isconverted into cyanamide dium sulfides also sodium fluor de may be usednitrogen; i v l l in that case if for instancie sodium fluoride Thus atand below 600 C. the reaction'accord- 2 and calcium cyanamide(containing 69/70% mg to thequationr v CaNCN) are heated invthe presenceof carbon g dioxide toabout 550 C., cyanate is also formed NazCO3-}-CaNCN=2NaCNOi-CaO according to the equations: l

cannot possibly develop towards the right hand 26 2 (d)ceNcN+2NaF=Ne2ucN+caFz side.

(b) Na2NCN+CO2=2NaCNO v Diiferent tests have in rea shown thatat (e)-CaNCN+2NaF+COz=2NaCN0+CaF and below 60090. a lnixture'of stoichiometricproportions of soda and calcium cyanamide (containing 69/7 0% CaNCN) isnot able-to react according to equation 7 2., After one hoursheatinguina nitrogen atmosphere the quantity Of nitrogen introducedunder the' form of Ca NCN can be recoveredas cyanamide nitrogenpracti--cally completely, s'aveiora certain loss of Z.5 -6%. taining sodiumcyanate and calcium carbonate If Contrast fi f lmentlonedr according tothe equations: y l above 15 t fi 170-600 Cf Current of carbondiox de,then apart from about; 7% f CaNCN-l-Na2COB=Na2NCN+CalCO3 losses, theWhole 'of the nitrogenintroduc ed (b Na2NCN+CQ2=2NaCNO underthe formofcyanamide is converted into v 40 (g) CaNCN+Na2CO3+CO2=2NaCNO+CaCOa cyanae i e i in a The specification of German a Na If the two modes ofoperation described above 490,247 describes that when heating a mixtureof are compared WiFh-eachther it be 9 alkali carbonates and alkalineearth cyanamides ceded that the p1e senc exerts to elevated temperaturesin the absence of Oxy a very favorable mfiuencelron t r o e:

dation agents alkali cyanates are formed actween Soda a ci a decordingto the equation:

It has further been ascertained that the sodium compounds mentionedabove may be replaced, partly or altogether,- by sodium carbon: ate. Iffor instance a mixture of stoichiometric proportions of soda and calciumcyanamide, as above, is heated in a current of carbon dioxide to 600 0.,one obtains a reaction product con- For the sake of simplicitythisreaction may v also be regarded in this manner that the carbon (h)CaNCN+Na2COs= NaC O+ dioxide removes the calcium oxide, which hinhoweverthis reaction h cannot be equalled to 1 r h iormation o yanateQrprevents its forthe reaction g mentioned above. For in the re-Elation, r y h 16946131911 q td t0 qu action it there is alwaysobtainedia product conn dean d v l p to th t h nd s d A taining calciumoxide which is able, for instance It appeared obvious to carry out thereaction at 600 0., to again react with sodium cyanate of calciumcyanamide with soda at temperatures 65 under formation of cyanamide.above 600 C. to the end of causing, by the use of still highertemperatures, the reaction according to the equation:

Na2CO3+CaNCN=2NaCNO+CaO to develop more towards the right hand side.

Thus if a mixture of for instance. 106 parts by weight soda and 116parts calcium cyanamide (containing 69% CaNCN) is heated to 650 0.

it is true that a better conversion of the calcium cyanamide introducedis obtained, but the higher temperature causes undesirable'secondaryreactions to occur.

Besides sodium cyanate there is also formed sodium cyanide and moreoverthe loss of nitrogen is considerably greater than when heating themixture of these starting materials to 600 C. or below, whereby however,as described above, little or no cyanate is formed.

The formation of sodium cyanide and the losses of nitrogen are caused,amongst others, by the following secondary reactions, which arefavorably influenced by higher temperatures:

: dioxide offers great advantages as compared to the known mode ofproceeding, wherein the solid components react with each other in theabsence of oxydation agents.

The iniiuenceof the carbon dioxide guarantees a practically complete andconsiderably faster formation of cyanate, which is due not only to thedisturbance of the equilibrium mentioned above, but also to the heatdeveloped in the exothermic reaction:

CaO.-}-CO2='CaCOs iiltrenders it: further possible to cause theintroduced starting materials to react at such temperatures at which, inthe absence of carbon'dioxide, no or only very incomplete conversions ofthe cyanamide into cyanate take place;

Itrnay further be stated that heating ina carbon dioxide atmosphereleads to reaction products, which are practically free fromundesirable'compounds such asforinstance sodium cyanides, sodium andalkaline earth cyanamides and alkaline earth oxides.-

The sodium cyanate obtained can be separated ina simple manner, forinstance with'water, from the alkaline earth compounds, such as calciumcarbonate, formed in the'reaction and from other impurities contained inthe reaction mass. It is impossible for any alkaline earth compounds togo into the solution, since all of them were converted into compounds.insoluble in water.

The carbon dioxide may be caused to act on the mixture of the startingmaterials at normal pressure or at pressures above or below normal.

One may also use gases containing carbon dioxide, provided that they arefree from constituents adapted'to disturb the reaction, such as oxygenor, water vapor. Thus for instance smoke gases containing about-1W 18%CO2 and about ed 15 minutes to 550 C.

. sisting of 106 'parts soda for instance magnesium carbonate, whichdevelop CO2 Within the range of 350 to 650 C.

In practicing this invention, one may for instance proceed as follows:

Example 1 16.743 grams of a mixture consisting of 85 parts sodiumfluoride and 113 parts calcium cyanamide (containing 70.5% CaNCN) wereheatin a carbon dioxide current in such manner that no vacuum can be.formed. The reaction mass is then allowed to react further one hour inan atmosphere of carbon dioxide at 550 C. 1

After "this heat treatment were obtained 20.833 grams of a reactionproduct weighing 4.09 grams=24.5% more, which apart from 0.5% sodiumcyanide-and 1.5% cyanamide (calculated as CaNCN) contained 46.6% sodiumcyanate.

Thus 89.0% of the cyanamide nitrogen introduced is converted intocyanate nitrogen, while 5.5 of the cyanamide nitrogen used is lostduring the heating.

Example 2 14.096 grams of a mixture consisting of parts sodium sulfide(containing 99% NazS) and 113 parts calcium cyanamide' (containing 70.5%CaNCNXWere heated 15 minutes to 500 C. in a vigorous current of carbondioxide. Already at about 450 'C. the mixture of the starting productsavidly absorbed carbon dioxide. After the heat treatment at 500 C. thereaction mass was left a'further hour in an atmosphere of carbon dioxideat the same temperature.

Thereaction product obtained, which weighed 20.34 grams of 6.245 grams(44.2%)v more, contained after the 'conv'ersion,apart from 0.5%cyanamide (calculated as CaNCN and 5.5% Na2S2O3 40.4% sodium cyanate.

, Thus about 87% of the cyanamide nitrogen introduced were convertedinto cyanate nitrogen.

Example 3 16.920 grams of a pulverulent mixture con- (containing 99%NazCOfl and 116 parts calcium cyanamide (containing 9% CaNCN) wereheated, as described with reference to Examples 1 and 2, 15 minutes to550 C'Qin a current of carbon dioxide. The reaction product was thenleft another hour at this temperature in a slow current of carbondioxide. 1

After the reaction was obtained amass contaim'ng cyanate, which weighed20.402 grams or 3.482 grams (20.6%) more and which contained besides0.48% sodium cyanide and 3.3% calcium cyanamide-3'Z%= sodium cyanate.

76.5% of the ,cyanamide nitrogen introduced were thus converted intocyanate nitrogen. 11.2% did not, react, 1.3% were converted into NaCNand 11.0% cyanamide nitrogen were lost.

If, for the sake of comparison, the above mixture was heated in themanner describedabove in an atmosphere of nit1'og,ennot in a current ofnitrogenno sodium cyanate could be traced.

Example 4 in such manner'that no pressure below normal occurred. Themass was then left another hour to react further in a slow current ofcarbon dioxide. After the conversion were formed 21,265 grams of aproduct of reaction weighing 3.988 grams (23.2%) more, which contained0.69%

NaCN and 43% NaCNO. 91% f the CaNCN were V Example 15.55 grams of amixture of 166 parts soda and 116 parts calcium cyanamide (containing69% CaNCN) were heated as a powder during 15 minutes to 650 C., acurrent of carbon dioxide being allowed to act on the reaction mass soquickly that no vacuum could form.

The reaction mass was allowed to stand another 15 minutes at 650 C. in aslow current of carbon dioxide, whereupon the test was interrupted.After cooling there resulted 1922 grams of a reaction mass weighing 3.6?grams (23.6%) more, which contained, besides 0.5% sodium cyanide, 43.3%sodium cyanate. No cyanamide was present anymore. The above shows that91.5% of the calcium cyanamide introduced were converted into cyanate.

For the sake of comparison 16.725 grams of the above mixture of startingmaterials were heated, also as a powder, 15 minutes to 650 C. in anitrogen atmosphere and held another 15 minutes at this temperature asabove. The result of this test was a reaction product weighing 16.639grams or 0.5% less, which contained 2.36% sodium cyanide, 21.2% calciumcyanamide and 12.8% sodium cyanate. The cyanamide nitrogen was thusconverted as follows: 5.3% into NaCN; 22% into NaCNO; 58.5% remainedcyanamide nitrogen and 14.3% got lost.

Various changes may be made in the details disclosed in the foregoingspecification without departing from the invention or sacrificing theadvantages thereof.

I claim:

1. The process of producing products containing sodium cyanate, whichcomprises reacting, at a temperature ranging between 450 and 650 C., analkaline earth cyanamide with a. sodium compound of the groupconstituted by the sulfide, the fluoride and the carbonate, with asupply of carbon dioxide in a quantity which exceeds the amount ofcarbon dioxide absorbed during the reaction by the alkaline earthcompounds present by at least 11 grams for every 7 grams nitrogenpresent in the starting mixture in the form of cyanamide nitrogen.

2. The process of producing a product containing sodium cyanate whichcomprises reacting at a temperature ranging between 450 and 650 C.calcium cyanamide with sodium carbonate, with a supply of carbon dioxidein a quantity which exceeds the amount of carbon dioxide absorbed duringthe reaction by the alkaline earth compounds present by at least 11grams for every 7 grams'nitrogen present in the starting mixture in theform of cyanamide nitrogen.

3. The process of claim 1, in which the alkaline earth cyanamide isreacted with a mixture containin two difierent sodium compounds of thekind specified.

4. The process of claim 1, in which the reaction is carried through at apressure above normal.

HERMANN THEODOR JOSEF KGNIG.

